Circuits with high voltage capabilities have wide industrial applications, which include power management systems for use in automobiles. These circuits include power transistors (e.g., high voltage transistor) that operate at a high voltage range (e.g., above 100V) and may also include low voltage transistors that operate at a much lower voltage range (e.g., 1 v to 5V). To protect low voltage transistors from high voltage operations, the power transistor may adopt one or more isolation schemes. For instance, one isolation scheme involves forming an isolation structure around a power transistor. The isolation structure may include one or more terminal trenches in a peripheral region that surrounds a transistor region of the power transistor. During high voltage operations, the junctions between the peripheral region and the transistor region may experience a heightened electrical field density, thereby causing a reduction in breakdown voltage. And in certain situations, the reduced breakdown voltage may lead to low level current leakage from the transistor region.